![]() Regular expressions use special characters in the PATTERN string to match a wider array of strings. (That's what the "re" in "grep" stands for). The true power of grep is that it can match regular expressions. Using regular expressions to perform more powerful searches Notice that the directory name is included for any matching files that are not in the current directory. Let's change our FILE name to an asterisk (" *"), so that it matches any file or directory name, and not only HTML files: We can extend our search to subdirectories and any files they contain using the -r option, which tells grep to perform its search recursively. Notice that each line starts with the specific file where that match occurs. When the command is executed, the shell expands the asterisk to the name of any file it finds (in the current directory) which ends in ". Instead of specifying product-listing.html, we can use an asterisk (" *") and the. If we have multiple files to search, we can search them all using a wildcard in our FILE name. Searching multiple files using a wildcard Using the -i option, grep finds a match on line 23 as well. What if "our products" appears at the beginning of a sentence, or appears in all uppercase? We can specify the -i option to perform a case-insensitive match: Performing case-insensitive grep searches Our matching line is prefixed with " 18:" which tells us this corresponds to line 18 in our file. If we specify the -n option, grep will prefix each matching line with the line number: It will be even more useful if we know where the matching line appears in our file. Viewing line numbers of successful matches If we use the -color option, our successful matches will be highlighted for us: For more information, see: Regular expression quick reference. Other characters have special meanings, however - some punctuation marks, for example. In the above example, all the characters we used (letters and a space) are interpreted literally in regular expressions, so only the exact phrase will be matched. ![]() Process IDs which match the selection criteria to stdout.The PATTERN is interpreted by grep as a regular expression. Pgrep looks through the currently running processes and lists the Pgrep, pkill - look up or signal processes based on name and other Instead, use pgrep which is designed to do precisely what you want: NAME As is so often the case, there's an app for that!ĭon't use grep + ps. This renders the elenium trick useless since what is actually passed to grep is selenium and not elenium so the grep will match itself.Īll this, however, only happens because you're not using the right tool for the job. Because you haven't quoted the expression you gave to grep (because you used elenium and not 'elenium' or "elenium"), the shell will treat it as a glob and expand it to the matching file name. This becomes more complicated if, as seems to be the case for you, you have a file called foo in your current directory. However, the grep process showing up in the ps results will have the string oo and is, therefore, not found by grep. Since the only character in the brackets is f, oo is equivalent to foo. Since grep works with regular expressions, it will treat as "any character in the list of characters inside the brackets". ![]() You either add a grep -v grep at the end of the pipe, or you use grep oo instead. There are two common, if convoluted, workarounds for this. Running ps aux | grep foo is problematic since the grep foo command itself will match foo and so appear in the output. ![]() The problem here, as perceptively figured out, is that the shell is expanding the glob characters in your search string to a matching filename before passing the string on to grep.
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